1. Field of the Invention
The present invention relates to control valves and, in particular, to metering valves.
2. Description of the Related Art
Fluid valves are well known mechanisms that are used to control the flow of a fluid (e.g., gas or liquid) through a conduit. A metering valve is a type of valve that provides precise control of the amount of fluid flowing through a conduit. Metering valves are used in a wide variety of industrial applications in which precise control is desired.
One particular application for a metering valve is in the power industry. For example, metering valves are used to control the amount of fuel (e.g., natural gas) that is delivered to the combustion chamber of a gas turbine. To meet stringent pollution emissions, it has become increasingly desirable to precisely control of the amount of fuel entering the combustion chamber.
To further reduce pollutants and to increase efficiency, it is generally desirable to operate the combustion chamber at high pressures. However, the operating pressure of the combustion chamber may be limited by the available supply pressure of the fuel supplied to the combustion chamber. The supply pressure may be increased by replacing and/or adding additional compressors to raise the supply pressure. Alternatively and typically less expensive, the supply pressure can be increased by reducing the pressure loss through the metering valve. Such pressure loss is often referred to as pressure recovery and is determined by the ratio of the total pressure at the inlet of the valve over the total pressure measured at the outlet of the valve.
One type of metering valve is an angle metering valve. Such angle valves have an inlet and an outlet that have longitudinal axes that are not parallel to each other. The angle between the longitudinal axes are often determined by the position of existing conduits and/or space limitations. Ninety degrees is a common angle in angle valves. Turning the direction of the fluid through an angle valve typically results in decreased pressure recovery.
There is, therefore, a general need for an improved high recovery metering valve.